The highway, by C.J. Box

When two sisters set out across a remote stretch of Montana road to visit their friend, little do they know it will be the last time anyone might hear from them. The girls - and their car - simply vanish. Former police investigator Cody Hoyt has just lost his job and fallen off the wagon. Convinced by his son, who the girls were coming to visit, and his former rookie partner Cassie Dewell, he sets out for the girls' last known location

When two sisters set out across a remote stretch of Montana road to visit their friend, little do they know it will be the last time anyone might hear from them. The girls - and their car - simply vanish. Former police investigator Cody Hoyt has just lost his job and fallen off the wagon. Convinced by his son, who the girls were coming to visit, and his former rookie partner Cassie Dewell, he sets out for the girls' last known location

When two teens go missing during a clandestine car trip, alcoholic investigator Cody Hoyt is convinced by his son and former partner to search for answers before discovering similar disappearances on a remote Montana highway that point to the work of a serial killer